1. Field of the Invention
The present invention relates to a method and a device for automatic adjustment of the conveying means, normally a belt conveyor, for printed circuits in a machine for performing the electrical test.
2. Description of Related Art
As is known, electrical testing of an unassembled printed circuit consists in checking that all the nets present on the printed circuit board are insulated form one another and that there is electrical continuity between the points of each net. For this purpose special machines are used which, by means of suitable electrical contact grids, with interposed interfacing devices (adaptors or fixtures) establish connections with well-defined points of the printed circuit that is loaded on the machine.
Automation of testing of unassembled printed circuits is made difficult mainly because of the considerable differences in the items to be handled, which require a laborious initial calibration at the start of each work cycle with batches of different circuits.
Automation of the electrical test on printed circuits is achieved mainly by using a belt conveyor, comprising side belts that support the printed circuit on both sides, and transfer it from the loading area to the test area, and subsequently to the unloading area, disposed on the same number of machine modules.
The conveyor belts are carried on mobile rails that can be adjusted to the width of the printed circuit board to be tested. The better this adjustment, the better the machine will work.
This adjustment can currently be carried out either manually or from a keyboard.
Manual adjustment is done by means of mechanical devices, which allow the two side rails to be moved manually on guides, or by use of a flywheel, and locked in position according to the width of the printed circuit.
Adjustment through keyboard control is done by entering the data concerning the exact width of the printed circuit, data which is transferred to motors, which, by rotating screws for example, move the rails sideward on guides to place them in the correct position according to the width of the printed circuit to be tested.
In both cases this adjustment requires the intervention of the operator, and thus is subject to the risk of human error.
Moreover, said adjustment is somewhat complex and not absolutely precise.
The object of the invention is to eliminate the aforementioned drawbacks and increase the precision and adjustment of the distance between the rails supporting the side conveyor belts in a circuit board test machine.
According to the invention, adjustment of the rails takes place completely automatically.
Essentially, micro switches are disposed on the rails and act as sensors, which, following the independent movements of the respective rails, detect the position of abutments or fixed stops indicative of the width of the printed circuit to be tested, establishing the stopping position of the rails.
The adjustment is advantageously carried out in the test area of the machine, level with the bottom fixture, and said abutments or fixed stops are advantageously the side edges of the top plate of the fixture. Alternatively, said fixed stops can be the side edges of any other plate of the fixture, or of said printed circuit to be tested.
In practice, after having disposed the fixture suitable for testing the particular printed circuit in the test area, the two rails are spaced at the maximum distance and subsequently brought together so as to detect said fixed stops, something which normally happens at different moments, the moments when the rails stop in said positions to be subsequently moved apart by a pre-established fixed length, so as to be disposed at the optimal distance for conveying the printed circuit to be tested.
Since the machine is built in modules, the rails of the other modules (loading station, unloading, etc.), which are provided with special sensors that detect the exact position of the already adjusted adjacent rails, are subsequently adjusted.